Genotypic Differences In Cadmium Tolerances Of Wheats And Their Mechanisms

A hydroponics experiment was set up to cultivate wheats which treated by four Cd concentrations, the concentrations were 0, 30, 60, 90μmol/L, was carried out to study bioeffects of cadmium on wheats, Cd absorption and accumulation, even dicussed Cd tolerance of different genotypic wheats. After that, a field experiment was set up, which using 6 genotypic wheats with different Cd tolerances treated by four Cd concentrations, such as 0, 10, 50, 100 mg/kg, to study effects of cadmium on their growthes, biomasses and yields in filling stage, discussed characteristics of Cd and other metallic elements absorbed and distributed in wheats, and revealed physiological and biochemical mechanisms. The main results are as follows.Firstly, there was a difference on effects of Cd on growthes and biomasses of seedlings, however, their average values were descending with Cd concentration ascending. The low Cd concentration promoted a part of wheats growing more quickly and accumulated more biomasses than controls', both growthes and biomasses of wheats exposed in middle and high Cd concentrations were less than controls'. As a whole, Cd depressed growthes, biomasses, leaf area indexes and accumulations of nitrogen of wheats in filling stage, to make matters worse, the yields of wheats were depressed because of Cd. The degrees of depressions were different among genotypics, genotypics with low Cd tolerance beared more poison from Cd than genotypics with high Cd tolerance.Secondly, contents of chlorophyll in flag leaves, soluble sugar in flag leaves and grains, soluble protein in flag leaves and grains and amylum in grains were depressed by Cd. Orders of relative values of soluble sugar in grains, amylum in grain and soluble proteins were different from Cd tolerances'. The contents of glutelin, HMW-GS and LMW-GS were on a descending trend on the whole, however, the ratio of HMW and LMW on an ascending trend. The results indicated that processing quality of grains treated by Cd became worse, and there were some relations between Cd tolerances and grains processing quality.Thirdly, POD activities of leaves in most of seedlings enhanced with Cd concentration ascending and treated time extending. Prolines of leaves in all seedlings were enhancing with different velocities. During filling stage, a part of wheats'POD and SOD activities enhanced in low Cd concentration, on the while, the POD and SOD activities were restrained. The isozymogram of POD and SOD indicated that effects of Cd on POD and SOD happened in enzyme protein synthesis stage.Fourthly, during seedling stage, Cd contents in up ground part and down ground part were increasing when aggravating Cd stress level, and Cd contents in down ground part were more than up ground part's. The highest Cd accumulations were not in highest Cd concentration, but in middle concentration. Most of Cd accumulated in down ground part. In filling stage, Cd content of each organ increased when the Cd concentration ascend. The highest accumulations of each organ happened in different Cd concentrations, because they affected by biomasses and Cd contents of the genotype's organ. Both orders of Cd contents and accumulations in organs were grains > stem-sheathes> leaves. As a whole, other metallic elements, such as Zn, Mn, Cu, Fe, their contents and accumulations in wheats were depressed.Last, the order of Cd tolerances of seedlings is Yumai 949 > Luohan 6, Yumai 25 > Zhongyu 10 > Xinmai 21 > Aikang 58, Xunong 5 > Yumai 18 > Luomai 23, and the order of Cd tolerances showed in filling stage is Luohan 6, Zhongyu 10> Xinmai 21 > Aikang 58> Yumai 18 > Luomai 23. There was no difference between Cd tolerances showed in seedling stage and filling stage.